Depending on what you're trying to do one of the "captive" ping urls works eg http://captive.apple.com
This is the url that apple devices ping to get the login box up for things like hotel wifi. There's a mozilla one also which is http://detectportal.firefox.com/canonical.html [1] , but that returns a redirect which may or may not work for your use case.
This is the url that apple devices ping to get the login box up for things like hotel wifi. There's a mozilla one also which is http://detectportal.firefox.com/canonical.html [1] , but that returns a redirect which may or may not work for your use case.
[1] https://support.mozilla.org/en-US/kb/captive-portal